BR Double blastpipes

A stated aim of the BR Standard designs was to maintain rather than improve on the performances of existing pre-nationalisation classes and not necessarily to improve on their fuel consumption either. The Britannias were intended to compare with the Class 7 types: Royal Scots, V2s, Castles and not the big Pacifics. Fitting a double chimney - or more likely a Kylchap - might allow them to do this but then leave a hole in the Class 7 provision. And what would be the implications for additional wear and tear and, yes, increased maintenance costs?

The professional engineer considers the design package from many viewpoints of which performance output is but one. Unfortunately, the enthusiast sees that performance output as the be-all and end-all and the other criteria should be sacrificed to achieve the maximum. Possibly the biggest example of this was their disappointment that 9Fs were not allowed to work passenger trains at 90 mph irrespective of the damage they would inflict on themselves, track and other infrastructure while so doing.

 

Totally agree, I wasn't advocating for a dc Brit simply noting that if capability was improved that would take it into a notionally higher power category.
Or more in hand for occasional extremis.

 

Alas for the Britannia is already insufficiently robust to handle the power output it already produces, making that output more sustainable would only exacerbate those issues.

 

I'd be grateful for this to be expanded please

 

Several Problems with Brits to my mind were adaptations from other locos that were found wanting on a 2 Large Cylinder as opposed to 3 cylinder loco.
The Slide bars Lner/ Bullied pacific Laird type ... unsuficiently robust/supported for a 28inch stroke
Wheel axle interface - only upto the job when executed perfectly under careful supervision
Frame design - Influenced by Bulleid pacifics with frames moved into centre lines of horn guides, but lack of suppport along bottom of frames leading to cracking, remedial welding on Brits, design improved for 71000 and later batches ( which never materialised).
Hindsight is a marvellous thing but a 3 Cylinder/Caprotti Double chimney Britannia ( so its 71000 with a smaller Firebox) would have been a better performing /balanced loco. Similarly a Brit with a 250psi Clan Boiler, possibly a double chimney and slightly smaller cylinders a more resilient one ?
Footnote ( wait for it) The former would have been up there with the West country/BB's and A3's,
the latter would actually have been better for mixed traffic purposes as a5ft 3 2-8-2 .

 

You need to look at the 9Fs and the frame design on that Class.

 

dont have anything to hand here;, did they have the combined springhanger stretcher subframes ? Think the shallower frames , smaller wheels , longer connecting rod went along way to mitigating some of the 'racking' forces that the Pacifics were subject to ,,,

 

Thank you for that, new knowledge!
As you say hindsight is wonderful, but it's worth noting that the Britannias were intended as mixed traffic locomotives as were most of the BR standard designs (but an oddity of history is that the 9F was intended as a specialist freight engine but wasn't one of the standard series and more of them were built than any other Riddles engine!).
Consequent to the mixed traffic ethos and to aid a rigid standardisation regime all the standards were designed with the intention of getting good performance at moderate steaming rates. This led to using the absolute minimum of cylinders for the expected duties hence the use of two on the Britannias. Again in retrospect it might have been better to have three smaller cylinders but that was the reason that two were chosen.
I'm not at all sure about Caprotti in the British context. All well and good in their Italian context to improve elderly Victorian engines, but for a modern engine I think they're an expensive solution to an insignificant problem. And, if they go wrong the result can be catastrophic and very expensive.
Anyway thanks for your post, most appreciated.

 

The 'significant' problem was how to actuate an inside cylinder without inside valve gear. BR Caprotti was i think reasonably successful on the Standard 5's, but as you say unneccesary/ expensive. Someone with a talent for it might one day compare the time out/expense for valve gear repairs/ resetting for the two types to see if the reason for fitting it really was justified. Interesting that the Caprotti 5's had an additional slide bar anchor point - but then why have expensive gear that doesnt need adjustment between overhauls if the cylinder rings need replacing frequently anyway. Love to see the surviving Caprotti 5 Given a double chimney and 'unleashed' on the mainline but i think that time has passed.

 

The frame arrangement of the 9Fs was completely re-designed during construction. From 92050 (stated on drawings) or 92097 (stated in book records) all the Crewe built 9Fs were fitted with cast hornblocks held in place by cold turned rivets and cast combined spring hangers and stretchers. I will have to check whether this applied to any of the Swindon bult locos, but I think it did.

 

Have a little involvement with the Clan Project and my queries on that design/construction have all been dealt with thoroughly and professionally, but i have never liked the idea of those welded on horn guides...